A conventional plasma generator for forming a thin film on a substrate by plasma is disclosed in the Japanese Patent Application No. 60-1279578 (the U.S. patent application Ser. No. 692,145). The major surface of the substrates which are processed on the CVD generator, has electrically conductive portions such that the generator produces substantially uniform plasma. Two opposed electrodes are provided on either one of the major surfaces. A first radio frequency source and a second radio frequency source are electrically connected to the first and second electrodes, respectively. Hereinafter, the radio frequencies are called as high frequencies in this description. The first high frequency source is out of phase from the second high frequency source.
However, with this conventional CVD generator, a solid and fine thin-film which exhibits high corrosion-resistive and abrasion-resistive properties can not yet easily have been formed on the substrate.